Manufacture of globular powder

ABSTRACT

A method of preparing globular propellant powder wherein presized lacquer particles are entrained in a liquor suspending medium and forced to flow through a long section of tubing until the propellant grains are dewatered and rounded into spherical shape. The spherically shaped powder globules are then passed into a flash evaporator having a pressure lower than that in the dewatering and shaping conduit so that a portion of the solvent within the globules volatilizes. The remaining solvent is removed by passing the slurry through a final hardener consisting of several chambers. Each of these chambers are individually heated to increase the temperature of the slurry of powder granules as it moves through the column. The temperature gradient between adjacent chambers in the latter stages may be increased.

United States Patent Andrew et a1.

[ July 25, 1972 [54] MANUFACTURE OF GLOBULAR POWDER [73] Assignee: OlinCorporation [22] Filed: Nov. 20, 1969 [21] Appl. No.: 878,269

[56] References Cited UNITED STATES PATENTS 2,740,705 4/1956 ONeill..264/3 E 3,014,246 12/1961 Cook et al. ....264/3 E PrimaryExaminer-Benjamin R. Padgett Attorney-Donald R. Motsko. H. Samuel Kieserand William W. Jones 57] ABSTRACT A method of preparing globularpropellant powder wherein presized lacquer particles are entrained in aliquor suspending medium and forced to flow through a long section oftubing until the propellant grains are dewatered and rounded intospherical shape. The spherically shaped powder globules are then passedinto a flash evaporator having a pressure lower than that in thedewatering and shaping conduit so that a portion of the solvent withinthe globules volatilizes. The remain ing solvent is removed by passingthe slurry through a final hardener consisting of several chambers. Eachof these chambers are individually heated to increase the temperature ofthe slurry of powder granules as it moves through the column. Thetemperature gradient between adjacent chambers in the latter stages maybe increased.

10 Claims, 1 Drawing Figure PATENFEEJMS I972 h 3,679,782

INVENTORS EUGENE A. ANDREW HENRY S. HALVERSON BY WK 1% I hr/ .5 4r

ATTORNEY BACKGROUND OF THE INVENTION This invention relates generally tothe manufacture of propellant powder. More particularly, this inventionrelates to the manufacture of globular granules of smokeless powder.

US. Pat. No. 2,027,114, granted Jan. 7, 1936, discloses a process ofmanufacturing smokeless powder wherein a lacquer, comprising a smokelesspowder base in a solvent is formed into globules and solidified whilesuspended in a nonsolvent medium. Many variations have been added tothis basic process to control the size and density of the resultingpowder particles which are of a spherical or near-spherical shape. Thisprocess for manufacturing propellant powder has come to be known tothose skilled in the art as the globular powder process.

The globular powder" process as heretofore known is essentially a batchprocess. Being a batch process, it suffers from the disadvantage that itis relatively slow with the result that a large amount of equipment istied up at a given time. In addition, there is some variance in thefinal product from one batch to another.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide an improved process for the manufacture ofspherical or nearspherical grains of propellant powder base.

It is another object of the present invention to provide an improvedmethod of presizing and shaping particles of propellant powder toproduce spherical or near-spherical grains.

Yet another object of the present invention is to provide an improvedprocess for hardening globules of a lacquer of a powder base and solventto produce spherical or near-spherical particles of propellant powder.

Still another object of the present invention is to provide a continuousprocess for making spherical or near-spherical grains of propellantparticles.

A further object of the present invention is to provide an improvedprocess for making spherical or near-spherical grains of propellantpowder having a relatively high density.

A still further object of this invention is to provide an improvedprocess for making spherical or near-spherical powder grains in whichthe processing time is materially reduced.

In accordance with this invention, these and other objects areaccomplished, generally speaking, by passing a lacquer comprising apowder base in a solvent through a mechanical grainer which presizes thelacquer into particles of generally cylindrical shape. The presizedlacquer particles are immediately suspended in a liquor solution whichis a non-solvent for the powder base and substantially immiscible withthe lacquer solvent. The liquor/lacquer slurry is then forced to flowthrough a long section of tubing until the cylindrical grains aredewatered (by the presence of a dewatering salt in the liquor) androunded into spheres due to the inner molecular and interfacial forcesacting on the grain caused by elevated temperatures in the tubing line.Turbulance within the shaping line also assists in the shaping of thegrain and aids in preventing adhesion between individual grains.

To harden the lacquer globules in accordance with this invention, theliquor/lacquer slurry is maintained under pressure during the dewateringand shaping operation. The pressure is necessary in order to preventsolvent vaporization since the temperature in the line is above theboiling point of the solvent of the lacquer. The slurry is continuouslypassed from the dewatering and shaping line into a flash evaporatorwhich is maintained at a temperature approximately the same as that ofthe incoming slurry and at a pressure lower than that in the dewateringand shaping line. As the slurry enters the evaporator, the reducedpressure causes the solvent within the globules to rapidly migrate fromthe globules and volatilize. At this point, the grain becomes hard andresists further deformation. Although over half of the solvent in thegrain is removed in this operation, some solvent still remains. Toremove the remaining solvent in an expeditious manner, the slurry isfurther processed through a final hardener which consists of a secondevaporator having a plurality of chambers. Each of the chambers areindividually heated to increase the temperature of the slurry as itmoves through the column. This reduces the amount of time required toremove the solvent without causing deformation of the individualglobules. If desired, the temperature gradient between adjacent chambersin the later stages may be increased.

DETAILED DESCRIPTION In order that the invention may be furtherclarified, reference may be had to the drawing which diagrammaticallyillustrates the steps of the process and to the following detaileddescription. Unless otherwise indicated, all the proportions of thematerials used are given in parts by weight of the resulting mixture.

The lacquer is prepared by mixing together the smokeless powder base anda solvent in a mixing unit 2 equipped with an agitator 4. The smokelesspowder base is preferably nitrocellulose which may be in the form ofground and extracted FNl-I (flashless non-hydroscopic) powder which iswholly or partly purified or any water wet nitrocellulose. The onlyrequirement for the solvent is that it be a solvent for the smokelesspowder base and be substantially immiscible with the suspending medium.In the case where nitrocellulose is the smokeless powder base and thesuspending medium or liquor is an aqueous solution, such solvent mayinclude ethyl acetate, isopropyl acetate, butyl acetate, ethyl formate,methyl ethyl ketone, methyl isopropyl ketone, diethyl ketone andmixtures thereof and the like. A stabilizer for nitrocellulose such asdiphenylamine may be added to the vat 2 in a. small amount of about 0.2to 0.7 percent. a

The viscosity of the lacquer should be controlled to provide uniformextrusion and permit hardening of the grains without distortion.Generally, the viscosity may range from about 6 seconds to 17 seconds asmeasured by the falling rod method. The falling rod method entailsutilizing a 0.314 inch diameter stainless steel rod weighing 60 gramsand dropping it from the lacquer surface into the lacquer for a distanceof 2.31 inches. The time required for the rod to move this distance isthe viscosity in seconds. If the viscosity is too low, the shape of theresulting grains will be distorted. If the viscosity is too high, theparticles will not assume a rounded shape and will not have the requireddensity as they will be difficult to dewater. Although a viscosity of 6to 17 seconds may be used, 12 to 15 seconds is the preferred range formaking grains having a final size of 0.020 to 0.030 inch.

The ingredients in mixing unit 2 are agitated and brought to atemperature between about 60 to about 70 C. The agitation of the mixtureshould continue until the lacquer becomes homogeneous.

Concurrently with the preparation of the lacquer, a liquor which formsthe suspending medium is prepared by mixing together in a separate tank6 which is provided with an agitator 8, the proper suspending vehicle, aprotective colloid and a dewatering salt. As has been stated above, thesuspending vehicle should be a non-solvent with respect to the smokelesspowder base and also immiscible with the lacquer. For reasons ofeconomy, such vehicle is usually water. The protective colloid may beselected from any one of the following materials: cornstarch, gumarabic, animal bone glue, dextrine, bentonite or the like.

The dewatering salt is preferably selected from a water soluble metalsalt such as sodium sulfate, magnesium sulfate, aluminum sulfate, bariumnitrate, sodium chloride, sodium nitrate and mixtures thereof. However,any substance which actually dissolves in the non-solvent medium andwhich will alter the physical properties of the liquor with respect towater in the lacquer so that the water will migrate from the lacquerparticles into the suspending medium may be used.

Respective percentages of the various ingredients constituting theliquor may be: the suspending vehicle between about 85 and about 95percent, the protective colloid between about 0.5 and 1.5 percent, andthe dewatering salt between about 3.5 and 6 percent.

in addition, a solvent, usually the solvent employed in the preparationof the lacquer, may be added to the liquor in an amount of between about3 and about 6 percent to prevent migration of the solvent from thelacquer globules during the presizing, shaping and dewatering operation.The solvent may be added to the tank 6 or it may be metered into theliquor line.

The ingredients in the tank 6 are mixed together by means of theagitator 8 and heated to about 50 to about 65 C. The liquor is pumped bymeans of a pump 10 to the downstream 7 side of the presizing plate ofpresizing unit 12.

The presizing unit 12 comprises a presizing extrusion plate 14 having aplurality of orifices therein and a rotating knife 16 to cut theextrudate into cylindrical particles having a diameter-to-length ratioof approximately 1 to l. The lacquer is pumped by means of pump 18through the extrusion plate 14 and is cut into the appropriate sizeparticles by the knife 16. The liquor is pumped into the presizing unitat a point immediately above the extrusion plate 14. As soon as thelacquer is cut into cylindrical particles, the particles are immediatelyimmersed and suspended in the liquor to form a slurry. The slurry oflacquer particles and liquor is then forced through a dewatering andshaping line 20.

The dewatering and shaping line 20 may be a long section of tubingprovided with suitable means to raise and maintain the temperature ofthe slurry to between about 75 to 85 C. Such means may be in the formofa water bath in which the section of pipe or tubing is immersed, or bymeans of a coaxial tube, the inner one of which provides the path forthe slurry and the outer one 22 provides a path for steam or other fluidof proper temperature to pass in heat exchange relationship. A nozzle orconstruction 24 is provided in the outlet end of the line 20 so that theslurry up to this point is maintained between a pressure slightly aboveatmospheric and a pressure of three atmospheres. As the slurry travelsthrough line 20, the dewatering salt present in the liquor causesmigration of water from the lacquer globules resulting in a less porousparticle of higher specific gravity. In addition, the cylindricalparticles of lacquer tend to assume a spherical or near-spherical shapedue to the molecular and interfacial forces acting on the grain as wellas the turbulance within the line.

After the slurry passes through constriction 24 it enters a flashchamber or evaporator 26 which is provided with a suitable agitator 28.The flash chamber 26 is maintained at a temperature approximately equalto the temperature of the incoming slurry or slightly greater ifdesired. The pressure within the evaporator is less than the pressurewithin the dewatering and shaping line 20 so that the exposure of theslurry to the reduced pressure will cause the solvent to rapidly migratefrom the grain surface and volatilize. The volatilized solvent may bewithdrawn through outlet 30 by suitable means and recovered bycondensation. The length of time a particular grain stays in the flashchamber depends basically upon the level of the slurry contained thereinand may be anywhere from to 60 minutes. During the process, about 60 to80 percent of the solvent in the globule is removed and the grainbecomes relatively hard and resistant to further deformation.

After the appropriate interval of time, the slurry is passed to a finalhardener 32 which consists of a column comprising from about three tosix chambers 34-44 which are individually heated. Some or all of themmay have a progressively higher temperature so that the temperature ofthe slurry is increased as it moves through the column. The remainingsolvent is extracted from the grain during this operation and isvolatilized and recovered by condensation. The temperature gradiantbetween adjacent chambers may be increased in the final stages of thehardener.

If desired in the event ofa six chamber evaporator, the first threechambers may all be at the same temperature which may be about 2 to 4 C.above that of the incoming slurry. The fourth chamber may be 2 to 4 C.above the previous chamber, the fifth chamber 4 to 6 C. above thefourth, and the temperature raised about 8 or 9 C. in the final chamber.The important consideration being that the temperature gradient betweenadjacent chambers should be about the same in the beginning and then maybe increased in the later stages. If the temperature is raised tooquickly and too great an amount, the grains may become thermally shockedand distorted. The retention time of the grains within the finalhardener is between about 10 and 40 minutes depending upon the processconditions.

As the slurry passes from the column, it enters a catch box 46 whereinthe hardened spherical powder is separated from the liquor by means of asuitable screen 48. The hardened powder is now ready for furtherprocessing such as nitroglycerine impregnation, deterrent coating andthe like to provide a finished product. The liquor is cooled,reprocessed and cycled back to the graining chamber and the condensedsolvent is reused to make lacquer.

In order to further illustrate the invention, the following is adetailed description of a preferred embodiment of the entire process.All proportions are expressed by weight unless otherwise indicated.

A lacquer was prepared by adding 140 pounds of ethyl acetate, one poundof diphenylamine and 15 pounds of benzene to a mixer equipped with anagitator. The mixture was agitated and brought to a temperature of 65 C.FNH smokeless powder was added to the agitated mixture in the amount of70 pounds on a dry basis. The powder contained water in the amount of 7percent by weight of the nitrocellulose. The agitation was continued andthe lacquer brought to a temperature of 60 C. Agitation of the lacquerwas continued for about 1 hour until it reached a relative viscosity of15 seconds as measured by the falling rod method. The specific gravitywas approximately 1.03. The solvent ratio, i.e., the ratio of the ethylacetate to the dry nitrocellulose, was 2.2/1.

Concurrently with the preparation of the lacquer, a liquor was preparedby adding 896 pounds of water to a vat or tank equipped with anagitator. The water was agitated and 15 pounds of a protective colloidand about 0.04% of silicon antifoam B were added to the water over theperiod of 3 to 4 minutes. The colloid and water were mixed for 15minutes and the temperature thereof elevated to 60 C. Fifty pounds ofsodium sulfate was added over a period of l to 2 minutes. The liquor waspumped to a presizing unit at the rate of 9.90 pounds per minute. inaddition, ethyl acetate in the amount of 3 to 6 percent was metered intothe liquor line prior to the grainer to complete the preparation of theliquor.

The lacquer was pumped through the extrusion plate at the rate of 2.85pounds per minute where it was cut into cylinders having a length and adiameter of 0.022 inch. The cylinders of lacquer were immediatelyentrained in the liquor and passed into the dewatering and shaping linewhich comprised a pipe having an internal diameter of approximately inchand a length of 300 feet. The temperature of the liquor/lacquer mixturewas 60 C. as it entered the dewatering line and was heated to C prior toleaving and the pressure was maintained at about 20 psig.

The liquor/lacquer mixture was passed through the dewatering and shapingline at a rate such that a given lacquer particle remained in thedewatering line between about 5 and 10 minutes. At the end of this time,the lacquer particle had been rounded into a substantially sphericalshape.

The mixture of liquor and spherical lacquer particles entered anevaporator which was maintained at atmospheric pressure and about 80 C.The mixture was kept under constant agitation whereby the solvent wascondensed and removed at the rate of about pounds per hour along with aportion of the water. The mixture remained in this evaporator for about15 minutes.

The spherical particles along with the liquor passed into the firstchamber of the final hardening unit. The final hardening unit consistedof six chambers with the mixture in the first three chambers beingmaintained at 83 C., the mixture in the fourth chamber being maintainedat 86 C., the fifth chamber 91 C., and the final chamber 99 C. Themixture was passed through the final hardener at the rate of l 1.0pounds per minute and had a residence time of 30 minutes. After thefinal hardening treatment, substantially all of the solvent had beenremoved from the spherical powder particles and the particles werehardened. The mixture may then be passed through a screen to separatethe hardened spherical powders from the remainder ofthe liquor.

The hardened powder grains resulting from this process had an averagesize of 0.0235 inch and were all between the range of 0.016 inch to to0.028 inch with 95 percent of the particles being between 0.020 inch to0.025 inch. The average specific gravity of the powder grains was 1.55with all the grains having a specific gravity between 1.54 and 1.56.

It will be appreciated that one of the advantages of the presentinvention is the fact that by the use of a dewatering and shaping line,an individual particle can be shaped into a substantially spherical bodyin the order of 3 to minutes. In accordance with previous processes, atleast three hours was required to form the spherical particles anddewater the grain. In addition, the use of a flash chamber wherein onlya portion of the solvent is removed in combination with a finalhardening unit having a plurality of chambers which are maintained atincreasing temperatures reduces the time required to harden thespherical particles from about 5 hours to 1% hours. Moreover, thecombining of the various steps of the present process permits a trulycontinuous powder making operation resulting in a higher rate ofproduction of powder for a given amount of equipment.

What is claimed is:

1. In the art of making powder grains wherein discrete particles of alacquer of a smokeless powder base and a solvent therefor are formed andshaped into substantially spherical particles while entrained in aliquor suspending medium which is a non-solvent for said powder base andsubstantially immiscible with said solvent, the method comprisingplacing the shaped lacquer particles and said suspending medium under apressure and temperature which prevents vaporization of the solvent,passing said shaped lacquer particles while entrained in said suspendingmedium through a first evaporator which is maintained at a temperatureabove the boiling point of said solvent and at a pressure below thepressure to remove a por tion of said solvent from said shaped lacquerparticles and thereafter passing said lacquer particles and saidsuspending medium through a series of hating zones, at least some ofsaid zones having a higher temperature than the zone immediately beforeit.

2. In the art of making powder grains, the method comprisingcontinuously passing a lacquer ofa smokeless powder base and a solventtherefor through at least one extrusion orifice, cutting said lacquerinto discrete particles after it passes through said orifice, entrainingsaid discrete particles in a liquor suspending medium which is anon-solvent for said powder base and substantially immiscible with saidsolvent to form a slurry, continuously passing said slurry throughconduit means of a predetermined length and at a predetermined rate toshape said particles into spherical or near spherical shape, passing theresulting slurry of suspending medium and shaped lacquer particlesthrough a first heating zone having a lower pressure than said line anda temperature above the boiling point of said solvent and thereaftercontinuously passing the remaining slurry through a series of heatingzones at east some of which have a higher temperature than the precedingzone.

3. The method of clam 2 wherein the lacquer is cut into cylinders havinga length to diameter ratio of about 1 to l t form said discreteparticles.

4. The method of claim 2 wherein. the temperature of said conduit meansis maintained at a temperature above the boiling point of the solventand under a pressure sufficient to prevent vaporization of the solvent.

5. The method of claim 2 wherein at least half of the solvent is removedfrom the shaped lacquer particles during the passage thereof throughsaid first zone.

6. The method of claim 2 wherein said suspending medium contains adewatering salt to cause migration of any aqueous medium from saidlacquer articles as said particles pass through said conduit means.

7. The method of claim 6 wherein said suspending medium is an aqueousmedium.

8. In the art of making powder grains from a lacquer of a nitrocellulosebased powder and a solvent therefor, the method comprising passing saidlacquer through an extrusion plate, cutting said extruded lacquer intodiscrete particles, entraining said lacquer particles in a liquorsuspending medium which is a non-solvent for said powder base andsubstantially immiscible with said lacquer to form a slurry, passingsaid slurry through conduit means for a time and temperature sufficientto shape said lacquer articles into a substantially spherical shapewhile maintaining said slurry at a pressure above atmospheric, passingthe resulting slurry of shaped lacquer particles and suspending mediumthrough a first evaporator at at mospheric pressure and at a temperatureabove the boiling point of the solvent, and thereafter passing saidslurry through a series of heating zones all maintained at atmosphericpressure, at least some of said zones having a higher temperature thanthe zone immediately preceding it, and thereafter separating saidhardened powder grains fro said suspending medium.

9. In the art of making powder grains, the method comprising preparing alacquer of smokeless powder base and a solvent therefor, preparing aliquor of an aqueous medium, a protective colloid and a dewatering salt,extruding said lacquer through an extrusion plate having at least oneopening of predetermined size, cutting the extruded lacquer into lengthssuch that the length to diameter ratio of the resulting particles isabout 1 to I, immediately entraining said particles in said liquor toform a slurry and passing said slurry through a conduit for a timesufficient to cause migration of any aqueous medium from said lacquerparticles and to permit said particles to assume a substantiallyspherical shape, passing said slurry through an evaporator atatmospheric pressure and at a temperature above the boiling point ofsaid solvent, and thereafter passing said slurry through a series ofheating zones all having a temperature higher than said evaporator andat least some of said zones having a temperature greater than thetemperature of the zone immediately preceding it 10. The method of claim14 wherein a first group of heating zones of said series of zones ismaintained at a temperature about 2 to 4 C. above that of said firstzone, the next zone is maintained about 2 to 4 C. above said evaporator,the next zone about 4 to 6 C. above that of the previous zone, and thefinal zone about 8 to 9 C. above the previous zone.

UNITED STATES PATENT @TTTCT QEIIFICAEE We CQRECIIQN Patent No. 3 ,679,782 Dated July 25 1972 Inventor(s) Eugene A. Andrew and Henry J.Halverson It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

In Column 5, line 50, "hating" should read as --heating-.

In Column 5, line 16, please delete 'to" the second occurence.

In Column 6, line 3, "east" should read as --least-.

In Column 6, line 5 "clam" should read as --claim--.

In Column 6, line 6, "t" should read as --to--.

In Column 6, line 17, "articles" should read "particles".

In Column 6, line 29, "articles" should read --particles-.

In Column 6, line 38, "fro" should read -from-.

In Column 6, line 58, "14" should read "9".

Signed and sealed this 30th day of January 1973.

(SEAL) Attest:

EDWARD M. FLETCIIER,JR., ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents FORM PO-1050 (10-69) USCOMM-DC 60376-P69 a US,GOVERNMENT PRINTING OFFICE: I969 0-366-834 Patent No. 3,679,782 DatedJuly 25, 1972 Inventor(s) Eugene A. Andrew and Henry J. Halverson It iscertified that error appears in the above-identified pat ent and thatsaid Letters Patent are hereby corrected as. shown below:

In Column 5, line 50, "hating" should read as --heating--.

In Column 5 line 16, please delete "to" the second occurence.

In Column 6, line 3, "east" should read as --least--.

In Column 6, line 5 "clam" should read as --claim--.

In Column 6, line 6, "t" should read as --to--.

In Column 6, line 17, "articles" should read --particles--.

In Column 6, line 29, "articles" should read --particles--.

In Column 6, line 38, "fro" should read --from--.

In Column 6, line 58, "14" should read --9--.

Signed and sealed this 30th day of January 1973.

(SEAL) Attest:

EDWARD P I.FLETCIIER,JR. ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents FORM USCOMM-DC 60376-P69 .5. GOVERNMENT FRlNTlNGOFFICE I 1969 0-356-335

2. In the art of making powder grains, the method comprisingcontinuously passing a lacquer of a smokeless powder base and a solventtherefor through at least one extrusion orifice, cutting said lacquerinto discrete particles after it passes through said orifice, entrainingsaid discrete particles in a liquor suspending medium which is anon-solvent for said powder base and substantially immiscible with saidsolvent to form a slurry, continuously passing said slurry throughconduit means of a predetermined length and at a predetermined rate toshape said particles into spherical or near spherical shape, passing theresulting slurry of suspending medium and shaped lacquer particlesthrough a first heating zone having a lower pressure than said line anda temperature above the boiling point of said solvent and thereaftercontinuously passing the remaining slurry through a series of heatingzones at east some of which have a higher temperature than the precedingzone.
 3. The method of clam 2 wherein the lacquer is cut into cylindershaving a length to diameter ratio of about 1 to 1 t form said discreteparticles.
 4. The method of claim 2 wherein the temperature of saidconduit means is maintained at a temperature above the boiling point ofthe solvent and under a pressure sufficient to prevent vaporization ofthe solvent.
 5. The method of claim 2 wherein at least half of thesolvent is removed from the shaped lacquer particles during the passagethereof through said first zone.
 6. The method of claim 2 wherein saidsuspending medium contains a dewatering salt to cause migration of anyaqueous medium from said lacquer articles as said particles pass throughsaid conduit means.
 7. The method of claim 6 wherein said suspendingmedium is an aqueous medium.
 8. In the art of making powder grains froma lacquer of a nitrocellulose based powder and a solvent therefor, themethod comprising passing said lacquer through an extrusion plate,cutting said extruded lacquer into discrete particles, entraining saidlacquer particles in a liquor suspending medium which is a non-solventfor said powder base and substantially immiscible with said lacquer toform a slurry, passing said slurry through conduit means for a time andtemperature sufficient to shape said lacquer articles into asubstantially spherical shape while maintaining said slurry at apressure above atmospheric, passing the resulting slurry of shapedlacquer particles and suspending medium through a first evaporator atAtmospheric pressure and at a temperature above the boiling point of thesolvent, and thereafter passing said slurry through a series of heatingzones all maintained at atmospheric pressure, at least some of saidzones having a higher temperature than the zone immediately precedingit, and thereafter separating said hardened powder grains fro saidsuspending medium.
 9. In the art of making powder grains, the methodcomprising preparing a lacquer of smokeless powder base and a solventtherefor, preparing a liquor of an aqueous medium, a protective colloidand a dewatering salt, extruding said lacquer through an extrusion platehaving at least one opening of predetermined size, cutting the extrudedlacquer into lengths such that the length to diameter ratio of theresulting particles is about 1 to 1, immediately entraining saidparticles in said liquor to form a slurry and passing said slurrythrough a conduit for a time sufficient to cause migration of anyaqueous medium from said lacquer particles and to permit said particlesto assume a substantially spherical shape, passing said slurry throughan evaporator at atmospheric pressure and at a temperature above theboiling point of said solvent, and thereafter passing said slurrythrough a series of heating zones all having a temperature higher thansaid evaporator and at least some of said zones having a temperaturegreater than the temperature of the zone immediately preceding it 10.The method of claim 14 wherein a first group of heating zones of saidseries of zones is maintained at a temperature about 2* to 4* C. abovethat of said first zone, the next zone is maintained about 2* to 4* C.above said evaporator, the next zone about 4* to 6* C. above that of theprevious zone, and the final zone about 8* to 9* C. above the previouszone.